The present invention relates to an immersion nozzle for metal melts, more particularly steel melts, and a process for producing the nozzle from a starting mix containing alumina and boron nitride, using at least one fluxing agent, at least one binder and optionally other standard admixed materials, by mixing the starting mix with liquid, molding and drying the mixture and, if necessary, firing the resultant shaped body.
Immersion nozzles are employed for the further processing of metal melts, especially for the continuous casting of steel.
West German Patent 30 03 046 discloses a ceramic batch which is based on alumina or zirconia or silica, carbon and binders for producing such immersion nozzles, and which contains 5 to 15 weight % of calciumsilicon and/or ferrosilicon and/or boron nitride. The boron nitride is intended to achieve a lowering of the melting point of the solid oxidic suspensions, e.g., alumina constituents with a size of 1 to 30 mm, which are present in the steel, so that they become molten and do not adhere to the refractory wall. However, a mix of various refractory materials is not proposed in this West German Patent No. 30 03 046 and, furthermore, there is no showing of the grain size of the corundum (alumina) used.
West German Laid-open Application No. 34 39 954 discloses a refractory wear part for the casting of molten melts that is made from a mix of Al.sub.2 O.sub.3, graphite, a combination of fluxing agents and a carbon-containing binder as well as a metal powder, and in which the fired wear part is completely or partly raw-glazed and is thereafter fired under oxidizing conditions, if desired. However, only alumina is employed as refractory material for producing these refractory wear parts, and no boron nitride is used.
West German Patent No. 34 01 999 discloses immersion nozzles in which a layer of boron nitride is applied onto the surfaces coming into contact with the steel.
When using immersion nozzles, especially in the case of steel melts, the above-mentioned problem of adhesion of oxidic constituents contained in the steel melt arises, whereby clogging of the nozzle can develop, leading to interruption of the casing of the metal melts. However, the longest possible casting times are absolutely necessary for reasons of cost.
A further problem of immersion nozzles is their spalling resistance, which must be high enough so as to prevent cracking and premature replacement of the nozzles.